1. Field of the Invention
The invention relates to a process and apparatus for the treatment of infectious waste in a rapid, cost efficient manner, with materially less environmental impact than the historically practiced art. More particularly, the invention relates to an apparatus and method for the batch treatment of biologically contaminated medical waste, such as syringes, gowns, bedding, containers, bandages and other liquid or solid materials which may be contaminated with infectious bacterial and viral agents, or with organic contaminants such as chemopharmaceuticals, oxidizable solvents, and the like, in a fluidizing bed reactor utilizing gas oxidation.
The disposition of infectious waste is an issue which has received considerable attention among governmental environmental agencies and the public and within the waste disposal industry. Inappropriate disposal practices, as evidenced by infectious medical waste washing up on the beaches of oceans and lakes, as well as being found in ordinary trash containers in public areas, supports the concern that currently practiced treatment and disposal methods are inadequate to handle, in a safe, cost effective manner, the volume of infectious waste being generated today. A process to treat economically large volumes of infectious medical waste in an environmentally acceptable fashion not heretofore used to treat such waste, is therefore needed.
2. Description of the Prior Art
Historically, most infectious waste has been treated by incineration, with the incineration residue thereafter being landfilled or dumped in the oceans. However, recent studies performed on emissions generated from the combustion of medical waste, even from facilities equipped with advanced air pollution control equipment, have demonstrated consistent emission of priority metals, acid gases, and carcinogenic organics such as 2, 3, 7, 8 furans and dioxin. (United States Environmental Protection Agency, Hospital Waste Combustion Study, December, 1988). It is the potential toxicity of emissions from medical waste incineration which has driven the capital and operating cost of incineration and pollution control equipment beyond the reach of most hospitals needing to replace old, inefficient, uncontrolled units. Controversy relating to incinerator emissions has also resulted in substantial public opposition to the construction of private or commercial incineration facilities. The consequence has been that demand for the treatment of medical waste has exceeded available supply, and commercial incinerators have, in instances, overcharged the generators of medical waste. This creates an even greater potential for illicit disposal.
Another method traditionally used for decontamination involves steam sterilization in autoclaves. However, autoclaves are not appropriate for economically treating large volumes of infectious waste, and have questionable effectiveness on certain microorganisms. Further, autoclaves do not change the inherent visual appearance of waste, resulting in uncertainty and fear among those persons responsible for its subsequent handling. Many cases have been reported of autoclaved waste being rejected at landfills.
Others have attempted liquid chemical disinfection of medical waste. For instance, U.S. Pat. No. 3,926,379 teaches a continuous process method for the decontamination of solid items of comparatively small size, such as hypodermic syringes. This material is introduced through a feed tube to a hammermill, along with a disinfectant liquid delivered by pump. Pulverized solid waste then drops to a bag or drawer. Disinfectant drains from the bag and is reused. However, with this device, the potential for microbial aerosols exists, as well as the inability to assure that the disinfectant solution has not become neutralized and therefore inactive. Finally, the device is limited to solid, friable objects of small size; it is not suitable for bulk, loose wastes as received from hospitals.
U.S. Pat. No. 4,618,103 discloses a continuous process method for the treatment of solid medical waste by disinfectant fluid during and after introduction to a high speed hammermill. Waste is manually introduced through a rotatable door to a feed tube, and from there to a hammermill along with disinfectant solution. Waste drops to a settling/separation tank, from which disinfectant solution is discharged continuously to a sewer, and solid residue is removed manually. As in U.S. Pat. No. 3,926,379, this method appears intended for small, solid objects in limited quantity; it is not therefore suitable for large volumes of medical waste.
U.S. Pat. No. 4,619,409 teaches a continuous process method for the treatment of solid medical waste by disinfectant fluid during and after introduction to a high speed hammermill. Waste material is continuously conveyed to a second conveyor which operates an automatic door ahead of the hammermill. Milled waste drops to a settling/separation tank, from which disinfectant solution is discharged continuously to a sewer, and solid residue is removed manually. As in the previous patents cited above, this method utilizes a high speed hammermill to achieve particle size reduction. Hammermills are suitable when applied to friable materials, but in practice have not proven efficient or effective in achieving particle size reduction with non-friable materials, such as sheet plastic or woven synthetics, neither of which can easily be fractured at standard conditions. Sheet plastics and woven materials comprise a substantial percentage of contaminated medical waste. Further, the method disclosed by this patent is not readily suitable for tonnage quantities of medical waste, owing to the need for manual removal of milled waste from the settling tank, thereby placing humans in contact with the material. Further, as in the previous patents cited above, there is no ability to assure the effectiveness of decontamination on a continuous basis. Finally, as in the previous patents cited, there does not exist the ability to treat other liquid organic wastes typically found among medical waste, for instance chemopharmaceutical materials or solvents, prior to discharge to a municipal sewer.
Applicant's prior U.S. Pat. application Ser. No. 305,473 discloses an apparatus for the treatment of medical waste on a continuous process basis. However, applicant's prior apparatus is not suitable for gas oxidation using a fluidized bed reactor for the disinfecting of medical wastes, nor is there the ability for improved quality control of the treatment process with applicant's prior apparatus as there is with the batch treatment process of the instant invention.